In the field of monitoring brain activity the use of electroencephalograph devices (EEG's) is well known. EEG's are used to measure and record small electrical signals which occur on the surface of the scalp as a result of brain activity. Typically, an EEG system includes a plurality of electrodes attached at selected positions on the subject's scalp, a corresponding number of lead wires, and a processing console. Typically, each electrode is connected to the processing console via a separate lead wire. The processing console is provided for signal selection, amplification, and conditioning. Also included in EEG systems are means for measuring electrode impedance, calibrating equipment, and observing and permanently recording data processed by the processing console.
It is well known that the processing console and the observation and recording equipment are often incorporated within a single unit. The single unit, however, is too large to be easily transportable by the subject under observation. Further, because long wires between the electrodes and the processing console are impractical, the subject must remain relatively stationary when using most available EEG systems.
Some EEG systems have been developed to overcome the problem of the subject having to remain still during observation. These devices include portable recorders which may be carried by the subject under observation. These systems do not, however, include means for contemporaneous observation of the record. It is well known that such observation is often desired.
One method for making EEG measurements and contemporaneous observations more practical is to replace the wire links between the electrodes and the processing console with wireless links. Thus, situations such as those described above--i.e., when long wires might encumber other simultaneous attention needed by the subject or when the mobility of the subject might be impaired--would be at least partially resolved.
Other devices have been produced to monitor, process and record data received from the vital organs of a body. Typical of the art are those described in the following U.S. Patents:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 3,253,588 R. F. Vuilleumier, et al. May 31, 1966 3,859,988 C. C. Lencioni, Jr. Jan. 14, 1975 3,943,918 R. A. Lewis Mar. 16, 1976 4,089,329 L. A. Couvillon, Jr., et al. May 16, 1978 4,186,749 T. B. Fryer Feb. 5, 1980 4,245,645 P. M. Arseneault, et al Jan. 20, 1981 4,279,258 E. R. John Jul. 21, 1981 4,409,987 R. A. McIntyre Oct. 18, 1983 4,471,786 H. Inagaki, et al. Sep. 18, 1984 4,495,950 D. E. Schneider Jan. 29, 1985 ______________________________________
Of these patents, the U.S. Pat. Nos. 3,253,588 ('588); 3,943,918 ('918); 4,089,329 ('329); 4,186,749 ('749); and 4,471,786 ('786) patents disclose devices which incorporate telemetric transmittal of sensed data to a selected processing center. Each discloses a device using transmission over radio frequencies (r-f) using amplitude modulation (AM) or frequency modulation (FM) methods similar to those used for broadcast radio. The transmitted signals are thus subject to the same interference and distortion as broadcast radio signals.
It is well known that FM transmissions are more reliable than AM transmissions. However, it is also known that FM signals are subject to distortion and interference from signals broadcast from other stations. Though in the field of radio broadcasting these disturbances are mostly annoyances to signal receptors, in the field of EEG monitoring such disturbances will provide erroneous data concerning the brain activity of the subject. In this context, distortion and interference is detrimental to accurate analysis and is therefore undesirable.
Therefore, it is an object of this invention to provide a means for transmitting signals detected by electrodes placed on a subject's body to a signal processor using telemetric methods.
It is also an object of the present invention to substantially reduce the distortion and interference typically present in standard transmission of radio frequency signals.
Another object of the present invention is to provide an electroencephalographic monitoring and recording device wherein digital data communications is incorporated to provide accurate transmission of detected brain activity signals.
Still another object of the present invention is to provide a lightweight transmitter for amplifying and digitizing EEG signals from the electrodes.
Yet another object of the present invention is to provide a means whereby the data transmitted may be checked and verified to insure that data received by a receiving device is valid, and further that any invalid data received is ignored.